because since 2009 the engine hasn't been upgraded while on other cars it has. the z had 332hp or 350hp for the nismo and guess what... 2015 it still has the same.
think that answers your question.
you're welcome
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2 plus 2 times 2 = ? ... hint, it's not 8
Stillen CBE, Stillen Gen 3, TP's, Uprev tuned - 324whp/264tq